1. Field of the Invention
The present invention relates to a projection apparatus, a projection method, and a storage medium having a program stored thereon, capable of adjusting differences of color balances, which occur during a spoke period.
2. Description of the Related Art
In a Digital-Light-Processing (DLP [registered trademark]) projector apparatus which uses semiconductor light emitting devices, such as light emitting diodes (LEDs) and semiconductor lasers (LDs) for a light source, light emission efficiency greatly varies between a timing immediately after starting light emission from a device and a much later timing.
Therefore, consideration of variation of the light emission efficiency is significant in improving quality of projection images.
In this respect, for example, Jpn. Pat. Appln. KOKAI Publication No. 2007-094108 discloses a technology in which influence from thermal change of a light source is suppressed by adjusting brightness of light emitting devices of individual colors of an LED array, based on supplied power waveform information which cancels variation in luminance of the LED array within each field period for each color component, to thereby maintain projection images at high quality.
For a projector apparatus, there is a difficulty in changing colors momentarily at a specific timing. Commonly, a period is provided in which a plurality of light emission colors are temporarily mixed. The changing period in which a plurality of colors are mixed is called a “spoke period” in association with a single-plate-type DLP method which has been developed based on use of a color wheel as a prerequisite. According to the DLP method, mixed-color light which is generated during the spoke period is measured in advance and is used effectively.
A semiconductor light emitting device achieves a current value as a target value, for example, by using a current control technology, such as PID control. However, the semiconductor light emitting devices have rise and fall properties concerning light emission driving which vary depending on voltages to apply, temperatures, and individual specificity of the devices. In addition, the rise and fall properties of light emission driving as described above vary depending on a capacitor volume inside a circuit including the semiconductor light emitting devices, and individual specificity and drive statuses of elements such as low-pass filters.
As the rise and fall properties of semiconductor light emitting devices vary, the color of the mixed-color light also varies. Such variation of properties of rise and fall of semiconductor light emitting devices as described can not properly be covered with the technology disclosed in a patent literature described above. If an actual light emission amount during a spoke period differs from a light emission amount measured in advance, continuity of gradations of projected colors is lost and consequently causes a problem of deterioration in image quality.
Hence, in consideration of variation of light emission statuses of semiconductor light emitting devices used as light sources, there is a demand for providing a projection apparatus, a projection method, and a storage medium having a program stored thereon, which are capable of projection with constantly precise and high image quality, maintaining continuity of gradations of colors.